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Visitors gather beneath the Christ the Redeemer statue as Maracana stadium, site of the Olympic opening ceremonies, stands in the background on July 4, 2016 in Rio de Janeiro, Brazil. (Image: Getty Images)

It is thought the attacks planned were similar to those seen recently in Orlando, US, and France.

The source said that federal police had arrested members of a group that was preparing acts of terrorism.

It was unclear where the operation was taking place or what the specifics of the operation were.